an interaction between organisms (intraspecific) or between species (interspecific) in which fitness of one is lowered by the presence of another.

We’ve already talked about intraspecific competition!

Fitness is Reproductive Success

• survive to reproductive age
• find a mate
• produce (raise) offspring

If two species are using the same resource and share the same niche, they can’t coexist:

Species A eats Species B and C, if Species B increases, Species C is in trouble.

Serrouya et al. (2017)

Two species, \(N\) and \(M\).

\[{dN_1 \over dt} = r_1 N_1 \left(1-{N_1 \over K_1}\right)\]

\[{dN_2 \over dt} = r_2 N_2 \left(1-{N_2 \over K_2}\right)\]

each with its own \(r\) and \(K\).

Two species, \(N\) and \(M\).

\[{dN_1 \over dt} = r_1 N \left(1-{N_1 \over K_1} - \alpha {M\over K_1}\right)\]

\[{dN_2 \over dt} = r_2 N \left(1-{N_2 \over K_2} - \alpha { N_1\over K_2}\right)\]

• \(\alpha\) - effect of \(M\) on \(N\) … i.e. how many \(N_1\)’s does a single \(N_2\) cut things down by.
• \(\beta\) - effect of \(N\) on \(M\).

Limited space, Limited carrying capacity, Mutual animosity (periodic skewering and dropping on rocks) …. can they get along?

• Above the line, the numbers decrease
• Below the line, the numbers increase

To see species 1 drive species 2 to extinction.